This invention can be used on model aircraft in combination with the tow-release mechanism described in our co-pending U.S. patent application Ser. No. 09/413,199, filed Oct. 5, 1999, and/or with the automatic pilot system described in our co-pending U.S. patent application Ser. No. 09/413,200, filed Oct. 5, 1999. The combination of these three systems produces a model glider that has no mechanically moving parts, yet it is able to take-off, fly, and land in a user-selected pattern, and it is sturdy and durable.
This invention relates to model airplanes and other flying toys which have a fuselage and separable inserted wings, specifically to a connection system which holds the wings securely in a slot in the fuselage during normal flight but releases them in case of a crash in order to absorb the force of the impact.
Many model airplanes and other flying toys have non-flexible wings which are attached to the fuselage during operation but which are detachable for easier packaging and transportation as shown in U.S. Pat. Nos. 4,233,773, 4,272,912, and 4,714,444. In several models, the removable wings are inserted into a slot or recess in the fuselage, as seen in U.S. Pat. Nos. 3,935,664, 4,494,940, 4,698,041 and 5,853,312. Flying toys with flexible wings which can be easily folded for transportation, such as U.S. Pat. No. 5,947,785, do not typically have removable wings.
For a stable flight performance, it is important that the wings stay in place during flight without any significant ;movement, so most models described in the prior art utilize some kind of wing securing means. It case of a crash landing, however, it is beneficial if the wings are allowed some movement in order to lessen the momentum the fuselage must absorb. An ideal wing assembly system would hold the wings securely in place during take-off, flight and normal landing while it would release them in case of a crash.
The simplest wing assembly found in the prior art, especially in the case of models built of rigid plastic foam, is to fit the wings very tightly into a slot in the fuselage and, thus, rely on friction to keep them in place. Theoretically, this frictional fit should hold the wings securely attached during flight but it should release them in the event of a crash when the impact forces are greater than the friction forces. This would protect the plane from breaking. In reality, however, the frictional fit works only for a few separations and re-insertions of the wings. This is because the material on the attachment surfaces wears down, resulting in a loose fit. Therefore, the model becomes useless after just a few detachings of the wings, whether due to transportation or crash-landing, since its wings can now shift out of their normal positions during flight. Furthermore, before the tight fit wears away, it is very cumbersome to insert such wings into their proper positions.
To provide more secure attachment for the wings, most models described in the prior art rely upon an additional component to hold the assembly together. In U.S. Pat. No. 5,853,312, a firm adapter is used to secure the wings to the fuselage. The adapter is supposed to keep the wings in place even in the case of a crash landing. To address the issue of impact protection, the nose of the airplane has a specially designed buffer that absorbs some of the impact forces. The major disadvantage of this is that while the nose buffer might work on the specific airplane shown, it cannot be easily adopted to other designs. Another disadvantage is that it only protects the airplane in a straight ahead crash when the nose of the fuselage hits an obstacle. In practice, it is more frequent to have a crash where the wing hits an obstacle. In this case, the nose buffer would provide no protection.
Other models described in the prior art rely on an elastic member to secure the wings to the fuselage. In most cases, the elastic member is supposed to keep the wings in place in a crash but allow them some movement to relieve the stress on the assembly. The major disadvantage of this type of wing connection is that in case of a fast take-off or strong winds, the wings might shift out of their proper positions because of the elasticity of the connection. Also, most elastic materials tend to lose their strength with time, so the movement of the wings can become more pronounced with extended use.
One of the inventions that relies on this type of elastic connection is described in U.S. Pat. No. 4,272,912. Here, the use of flexible connecting rods is proposed to keep the wing permanently attached to the fuselage, while providing some stress protection to the wings in case of a crash. The main disadvantage of this system is that since the connecting members are elastic, they allow some movement to the wings in case of a fast take-off or strong winds, resulting in decrease flight performance. Another disadvantage of this approach is that it is applicable only to an airplance that has struts external to the fuselage for holding the wing to the fuselage. Therefore, it cannot be used in rigid foam planes where the wings are inserted into a fuselage cavity, which is the type of design the present invention is focused upon.
U.S. Pat. No. 4,494,940 to Gretz (1985) describes an elastic clip that fits across the fuselage and into holes in the wings. This approach, however, also has several unwelcome properties: (a) By design, the connecting clip allows the wings some movement with respect to the fuselage. Initially, the wing-fuselage connection is reinforced by a tight frictional fit, and the wings stay in place under normal conditions. When the frictional fit wears away, the wings can shift out of their correct position during a normal flight, even with the clip in place. (b) Also by design, each wing needs to have hole(s) to receive the connecting clip. This weakens the wing at its root, which is precisely the part of the wing that carries the greatest structural load, and is usually reinforced to sustain it. (c) To make the plastic clip fit flush with the adjacent surfaces, a recess might be formed across the top of the fuselage. This, unfortunately, weakens the fuselage. Because of its reduced cross-section, this is the part that is most likely to break in a hard landing, rendering the aircraft useless. (d) The inertia forces of a wing that comes to a sudden stop in a crash are transmitted to the connecting clip by the walls of the receiving hole. If the clip is made of a harder material than the wings are (as in the case of plastic foam airplanes), the holes in the wings become enlarged and distorted after a few crashes. Consequently, the wings are no longer held in their correct positions with respect to the fuselage.
Another example of the use of an elastic, member, in this case a spring, is given in U.S. Pat. No. 4,233,773. The wing has two pins or dowels located in the middle of the leading and trailing edges of the wing that are inserted into holes located in the middle of the fuselage. To join the wing to the fuselage, the user inserts the leading edge dowel into its fuselage hole and by sliding the wing forward he is able to insert the rear dowel into its fuselage hole. This forward sliding motion compresses a spring mounted inside the wing. Since the force of the compressed spring pushes the wing rearward it prevents the rear dowel from coming out of its hole, thus holding the wing securely to the fuselage. If the nose of the fuselage hits an obstacle, the inertia of the wing will be strong enough to overcome the backward force of the spring, the wing will then slide forward allowing the rear dowel to slide out of its fuselage hole. Thus the wing is separated from the fuselage avoiding damage in case of a crash. The main disadvantage of this system is that it only detaches the wing in a straight ahead crash when the nose of the fuselage hits an obstacle. In practice it is more frequent to have a crash where the wings hits an obstacle. When this happens the wing will be damaged since the wing dowels are inside the fuselage holes and this situation does not allow the wings to move laterally or rotate during a wing tip crash; therefore, the wing will not separate from the fuselage. Another disadvantage of this system is that it is not applicable to rigid foam airplanes that tightly insert the wings into a fuselage receptacle, since the wings cannot slide forward or backward inside such a tight fuselage receptacle.
There are designs in the prior art where the elastic member, typically a rubber band, is designed to keep the wings in place during flight, but it allows them to break away in case of a crash. An example of this approach is shown in U.S. Pat. No. 4,714,444. It is likely that such a rubber band allows some movement to the wings in case of a fast takeoff or strong winds, resulting in decreased flight performance. If this is to be avoided by frictional fit between the wing and the fuselage, material wear-down becomes a problem.
The above problems result from the use of frictional fit and/or an elastic connecting member for holding the wings in their flying positions. Consequently, these problems can be solved by eliminating (or significantly reducing) the frictional fit, and providing non-elastic means to secure the wings, which would break away in case of a crash.
The present invention provides an impact-absorbing wing connection system for a model aircraft that has wings which are inserted into the fuselage. The present invention addresses three major shortcomings in the prior art: 1.) when an elastic member is used to secure the wings to the fuselage, the wings can exhibit some movement during flight because of the elasticity of the connecting member; 2.)when the wings are kept in the fuselage even in case of a crash, the impact forces can significantly damage the aircraft; and 3.)when the wings are repeatedly inserted into and removed from the wing slot, the friction causes the surfaces to wear away and allow significant movement of the wings during flight. This latest issue is especially important for rigid foam airplanes. The novel concepts of the present invention are: 1.)it uses connecting links that are non-elastic to secure the wings to the fuselage to prevent any movement during flight; 2.)the non-elastic links are designed to break in case of a crash to release the wings; and 3.)it applies a low friction protective coating on the inserted portion of the wings to facilitate the separation of the wings and to reduce the wear between the contact surfaces.
In accordance with the present invention, a durable, impact-absorbing wing connection system for model aircraft and other flying toys of the type having disjoined wings that fit into lateral slots in the fuselage comprises means for reducing the friction while preserving the tight fit between the wings and the fuselage, a set of non-elastic break-away links to hold the wings securely in the fuselage during flight, and a corresponding set of connecting members on the fuselage and the wings, respectively, to which the break-away links are attached. The wings are placed into their proper flying positions easily, because of their low friction fit with the fuselage, and they are kept in these positions during normal flight by their tight fit and the non-elastic break-away links. In case of a crash, the inertia forces of the wings are conveyed to the break-away links by the connecting members. The strength of the break-away links is calibrated so that they snap upon a crash, releasing the wings. Because their reduced friction, the wings slide of the wing slots easily, absorbing the impact forces, and protecting the wings from breaking.
Accordingly, several objects and advantages of the present invention are:
(a) to provide a wing connection system, which uses no elastic members, so that the wings are kept firmly in place during high-speed take-off, flight, and landing;
(b) to provide a wing connection system, which releases the wings in case of a crash in order to absorb the impact forces, and does so without damaging any structural part but the designated break-away link;
(c) to provide a wing connection system, in which the wings can easily slide in and out of the fuselage without producing premature wear on the connecting surfaces, so that the initial tight fit is preserved even after repeated assemblies and disassemblies;
(d) to provide a wing connection system, which does not weaken the structural integrity of either the wings or the fuselage;
(e) to provide a wing connection system, which makes the assembly and disassembly of the wings simple and fast;
(f) to provide a wing connection system, in which the break-away link can be easily and inexpensively replaced; and
(g) to provide a wing connection system, which can be used on models made of soft material, such as molded plastic foam.
Further objects and advantages are to provide a wing connection system, which is inexpensive to manufacture, and which, at least in some embodiments, can be installed on many existing model airplanes by simple adhesive means. Still further objects and advantages. will become apparent from a consideration of the ensuing description and drawings.